A central characteristic of cancer cells is the ability of the cells to become deregulated in their normal function and subsequently undergo rapid division (tumor growth) and changes in their migratory behavior (tumor metastasis). Several signaling molecules along with components of their signaling pathways have been implicated as causative factors for, one of these being Wnt proteins. There is important evidence for a role of Wnt signaling in cancers as Wnt proteins can transform mammary cells and mutations in components of the Wnt signaling pathway such as 2-Catenin have been shown to play causative roles in cancers in humans. In fact, the first Wnt protein, Wnt-1, was identified as a factor when aberrantly expressed in the mammary gland resulted in breast cancer. We therefore propose that identifying the molecular components and understanding the mechanisms of Wnt signaling remains crucial for our understanding of human cancer formation. Studies have shown that Wnt signaling through the cytoplasmic protein Dishevelled (Dvl) induces the stabilization and nuclear translocation of 2-catenin (2-cat), which then regulates transcriptional induction of Wnt-target genes. However, the regulation of 2-cat nuclear translocation remains poorly defined and also the regulation of 2-cat transcriptional activity is not fully understood. This proposal is directed towards the characterization of a new modulator of Wnt signaling. We have identified this molecule termed DBP, for Dishevelled Binding Molecule, via a yeast-two hybrid screen using Dvl as a bait. In mammalian cells, DBP interacts with key components of the Wnt signaling pathway including Dvl and Casein kinase 1 (CK1), and antagonizes Wnt-stimulated transcriptional induction. Cellular localization studies of DBP demonstrate that this protein is normally present in both the cytoplasmic and nuclear compartments of cells. However, in response to Wnt stimulation, DBP becomes predominantly localized to the nucleus. Furthermore, DBP influences the subcellular localization of 2- cat, a crucial factor required for the transcriptional induction of Wnt-target genes. In vivo analysis of DBP during Xenopus development perturbs embryonic pattern formation and depletion of DBP prevents embryonic head formation. Based on our preliminary studies, we hypothesize that DBP is an essential component required for Wnt signaling. We propose two specific aims in this grant proposal and our studies are directed towards a biochemical, cell biological and in-vivo characterization of DBP to delineate its mode of action along with a recently identified effector for DBP. These studies will utilize mammalian culture cells and the Xenopus embryo as model systems. Towards this end, our studies are directed towards uncovering and understanding the role of these two new components of the Wnt signaling pathway. We propose that analyzing these new components will help to define the molecular nature of Wnt signaling from the plasma membrane to the cell nucleus and ultimately lead to a better understanding of how deregulated Wnt signaling results in cancer formation. PUBLIC HEALTH RELEVANCE: Understanding the development of human cancers remains dependent on identifying key signaling molecules and their signal transduction pathways that contribute to this pathology. One key-signaling molecule that has been demonstrated to play causative roles in human cancer is the Wnt protein. Our studies are focused on understanding two new molecules that we have identified that function in the Wnt signaling pathway, and we propose that these studies can provide important new insights into cancer formation.